Fuel/air mixture and combustion apparatus and associated methods for use in a fuel-fired heating apparatus

Abstract

A fuel-fired furnace incorporates specially designed fuel/air mixing and combustion structures. The fuel/air mixing structure is of a mixing sound-attenuating design and includes a venturi having a perforated sidewall portion and being surrounded by a noise-damping housing chamber communicating with the interior of the venturi via its sidewall perforations. During use of the mixing structure, air is flowed through the venturi in a swirling pattern while fuel is transversely injected internally against the swirling air. The combustion structure includes a burner box housing into which the fuel/air mixture is flowed, combusted, and then discharged as hot combustion gas into and through the heat exchanger tubes. The fuel/air mixture entering the burner box housing initially passes through a non-uniformly perforated diffuser plate functioning to substantially alter in a predetermined manner the relative combustion gas flow rates through the heat exchanger tubes.

That which is claimed is: 
     
       1. A method of mixing fuel and air in a fuel-fired heating apparatus, the method comprising:
 providing a venturi structure having a longitudinal axis extending through its interior, sidewall perforations, and first and second opposite end portions; 
 forming around the venturi structure a chamber that communicates with the interior of the venturi structure through its sidewall perforations; 
 creating a flow of air that flows through the interior of the venturi structure from its first end portion to its second end portion while swirling about its longitudinal axis; 
 creating, via radially directed interior fuel jets, a flow of gaseous fuel that interiorly impacts and mixes with the swirling flow of air creating a fuel/air mixture in a direction transverse to the longitudinal axis; and 
 permitting the fuel/air mixture traversing the venturi structure to enter the chamber to damp pressure oscillations within the venturi structure in a manner attenuating fuel/air mixing noise generated within the venturi structure. 
 
     
     
       2. The method of  claim 1 , wherein the venturi structure comprises a sidewall that extends from the first end portion to the second end portion such that the sidewall tapers from the first end portion and the second end portion towards a substantially mid-portion of the venturi structure. 
     
     
       3. The method of  claim 2 , wherein the sidewall perforations are circumferentially disposed around the side wall from adjacent the venturi inlet to the substantially mid-portion of venturi structure. 
     
     
       4. The method of  claim 1 , wherein the chamber laterally extends around the venturi structure and communicates with an interior of the venturi structure through the sidewall perforations such that the fuel/air mixture traversing the sidewall perforations enters and fills the chamber to create a noise attenuating volume that damps the pressure oscillations within the venturi structure in a manner that attenuates the fuel/air mixing noise generated within the venturi structure. 
     
     
       5. The method of  claim 1 , wherein a vane structure disposed on a housing that houses the venturi structure causes the flow of air to swirl about the longitudinal axis of the venturi structure. 
     
     
       6. The method of  claim 2 , wherein the chamber extends from the first end portion of the venturi structure to the second end portion of the venturi structure. 
     
     
       7. A method of sound-attenuation in a fuel-fired furnace, the method comprising:
 creating a flow of air through an interior of a venturi structure having (i) a longitudinal axis extending through its interior, (ii) sidewall perforations, and (iii) first and second opposite end portions, while swirling about its longitudinal axis; 
 creating a flow of gaseous fuel that impacts and mixes with the swirling flow of air creating a fuel/air mixture in a direction transverse to the longitudinal axis, wherein the flow of fuel is provided by radially directed interior fuel jets disposed within the first end portion of the venturi structure; and 
 dampening pressure oscillations within the venturi structure, via a chamber disposed around the venturi structure, wherein the chamber is in fluid communication with the interior of the venturi structure through its sidewall perforations such that the fuel/air mixture enters the chamber, in a manner effective to attenuate fuel/air mixing noise generated within the venturi structure. 
 
     
     
       8. The method of  claim 7 , wherein the venturi structure comprises a sidewall that extends from the first end portion to the second end portion such that the sidewall tapers from the first end portion and the second end portion towards a substantially mid-portion of the venturi structure. 
     
     
       9. The method of  claim 8 , wherein the sidewall perforations are circumferentially disposed around the side wall from adjacent the venturi inlet to the substantially mid-portion of venturi structure. 
     
     
       10. The method of  claim 9 , wherein the chamber laterally extends around the venturi structure and the fuel/air mixture traversing the sidewall perforations enters and fills the chamber to create a noise attenuating volume. 
     
     
       11. The method of  claim 10 , wherein the swirling of the flow through the interior of the venturi structure about its longitudinal axis is caused by a vane structure. 
     
     
       12. The method of  claim 7 , wherein the fuel/air mixture exiting the venturi structure flows through a secondary fuel/air mixing structure before entering a fuel/air mixture burner box housing for combustion therein. 
     
     
       13. The method of  claim 12 , wherein the fuel/air mixture has enhanced mixing of the fuel/air mixture to be combusted desirably reduces a level of NOx emissions created by the furnace during firing thereof. 
     
     
       14. A method for reducing a NOx level of discharged combustion gases in a fuel-fired heating apparatus, the method comprising:
 creating, via a vane structure, a flow of air through an interior of a venturi structure having (i) a longitudinal axis extending through its interior, (ii) sidewall perforations, and (iii) first and second opposite end portions, while swirling about its longitudinal axis; 
 creating, via radially directed interior fuel jets, a flow of gaseous fuel that mixes with the swirling flow of air in a direction transverse to the longitudinal axis; and 
 dampening pressure oscillations within the venturi structure, via a chamber disposed around the venturi structure, wherein the chamber is in fluid communication with the interior of the venturi structure through its sidewall perforations; 
 flowing a fuel/air mixture exiting the venturi structure through a secondary fuel/air mixing structure, wherein the fuel/air mixture is permitted to enter the chamber disposed around the venturi structure through the sidewall perforations; and then 
 flowing the fuel/air mixture into a burner box of the fuel-fired heating apparatus, 
 wherein the secondary fuel/air mixing structure is effective to further mix the fuel and air by providing further residence time for the fuel/air mixture created in the venturi structure housing, which is effective to reduce the level of NOx emissions created by the fuel-fired heating apparatus during firing thereof. 
 
     
     
       15. The method of  claim 14 , wherein the secondary fuel/air mixing structure comprises a diffuser plate. 
     
     
       16. The method of  claim 15 , wherein the burner box is coupled to plurality of heat exchanger tubes comprising one set of heat exchanger tubes and another set of heat exchanger tubes. 
     
     
       17. The method of  claim 16 , wherein the diffuser plate comprises a first set of holes and a second set of holes, wherein the first set of holes are larger than the second set of holes, and wherein the diffuser plate is disposed such that the first set of holes face the one set of heat exchanger tubes and the second set of holes face the one set of heat exchanger tubes and the another set of heat exchanger tubes. 
     
     
       18. The method of  claim 14 , wherein the sidewall perforations are circumferentially disposed around the side wall from adjacent the venturi inlet to the substantially mid-portion of venturi structure. 
     
     
       19. The method of  claim 18 , wherein the chamber laterally extends around the venturi structure and the fuel/air mixture traversing the sidewall perforations enters and fills the chamber to create a noise attenuating volume. 
     
     
       20. The method of  claim 16 , wherein the heat exchanger tubes are arranged in a linear array and have inlets in fluid communication with the interior of the burner box through the outlet end of the burner box for receiving the hot combustion gas generated within the interior of the burner box, and wherein the outlets of the heat exchanger tubes are coupled to a collector box.